Photographic processing of silver halide color photographic materials generally consists of color development and desilvering. In desilvering, reduced silver resulting from development is oxidized with a bleaching agent and then dissolved with a fixing agent. Bleaching agents mainly include ferric ion complexes (e.g., aminopolycarboxylic acid-iron (III) complex salt), and fixing agents mainly include thiosulfates.
Photographic processing of black-and-white light-sensitive materials consists of development and removal of unexposed silver halide. Unlike the processing of color photographic materials, the black-and-white photographic materials are subjected to fixing without bleaching. In this case, too, thiosulfates are usually used as a fixing agent.
With the recent tendency toward reduction of replenishment, it has been demanded that each processing bath has improved stability. With respect to a fixing bath, since commonly employed thiosulfates undergo oxidative deterioration to form a precipitate of a sulfide, a sulfite is added as a preservative for prevention of oxidation in most cases. As a rate of replenishment is further reduced, a further improvement in fixing bath stability is demanded. However, the demand can be no more met by a mere addition of an increased amount of a sulfite preservative because of a limit of solubility and undesired precipitation of Glauber's salt accompanying oxidation of the sulfite.
U.S. Pat. No. 4,378,424 and JP-A-57-150842 (the term "JP-A" as used herein means an "unexamined published Japanese patent application") propose to use meso-ionic 1,2,4-triazolium-3-thiolate compounds as a fixing agent taking the place of thiosulfates, but no detailed study was devoted to other meso-ionic compounds.
JP-A-1-201659 discloses addition of a meso-ionic thiolate compound to a fixing bath or a bleach-fix bath as a bleaching accelerator, and JP-A-2-44355 discloses addition of a 1,2,4-triazolium-3-thiolate compound to a fixing bath as a fixing accelerator. However, these publications contain no reference to use of the specific meso-ionic compounds according to the present invention shown below as a fixing agent nor yet the effects purposed by the present invention.
Other known meso-ionic compounds include those disclosed in U.S. Pat. Nos. 4,003,910, 4,675,276, 4,624,913, and 4,631,253, JP-A-62-217237, JP-A-64-3641, JP-A-60-144737, JP-A-62-253161, JP-A-62-287239, JP-A-61-176920, JP-A-62-96943, and JP-A-1-154056. These compounds have been developed for use as an additive to photographic materials or an additive to a developing solution, and there is no disclosure about the effects aimed by the present invention shown below.
On the other hand, improvement in image preservability has also been demanded. Studies have been directed to both materials of photographic materials and the final bath of processing but not yet reached sufficient results.
Thus, both of bath stability and image stability have not yet been improved to satisfaction, and it has been needed to take a drastic measure therefor.